update the host files to point to accessible docker container names for backends

added testing for this, including mock backend server.

dockerfiles/services/sslproxy/cli/exec

@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+set -e
+
+export DOCKER_HOST=${DOCKER_HOST:-'dkhost:2376'}
+
+docker exec $@
+#docker network inspect ingress